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  1. #1
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    Do I have a sticky piston or a warped caliper?

    My rear Avid 2007 Juicy 5 has been a very problematic brake. After the first week of riding the brake started squealing like a turkey in heat and to add insult to injury the turkey warble was accompanied with a violent vibration, which resonated through the frame. The only combination that cured the vibration was to switch out my 185mm rotor with a 160mm Clean Sweep G2 rotor and change over to organic pads-the turkey warble never stopped.

    Anyway jumping ahead one year to the present, this weekend I switched out my rear organic pads with new semi metallic pads and found that the pistons were very hard to push back into their cylinders. Specifically the outside piston was much more stubborn than the inside one. The rear brake piston seems to retract very slowly (not the lever) because bike is hard to pedal for a few seconds after the lever is released. Before I changed out the pads I noticed this hard to pedal phenomena-but could not pinpoint the cause.

    What is causing this problem? A) Dirt buildup between the piston and the cylinder? B) A worn-out or defective piston seal that is not springing/returning the piston back in the cylinder or C) a warped caliper that is hanging up the free movement of the brake pads?

  2. #2
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    Reputation: SteveUK's Avatar
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    Could be a failed seal, a dirty seal or just time for a bleed or fluid flush. Removing the pads and extending the pistons as far as possible then cleaning them with DOT fluid or a silicone spray (the better option) should free up the seal. If not, try a bleed. Depending on your mileage/use, the DOT could be due a change. If the fluid you draw out as you bleed is notably thicker and darker than clean fluid, then continue and draw it all through for fresh stuff. If cleaning the seals and changing fluid doesn't do the trick, it may be time to consider a seal change.
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  3. #3
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    Three months ago I flushed my system with new DOT 4 brake fluid and bled my brakes. The rear brake lever has very little free play before the pads engage the rotor; however my front brake feels like it did when it was new--lots of free play before the pads touch the rotor. Did I overfill the rear brake's MC? The brakes have been in service for one year and have less then 500 miles on them.

    So how do I clean my pistons? A) Do I remove the caliper from the bike and squeeze the lever until the pistons are few mm apart and clean the pistons with isopropyl alcohol or brake fluid then push them back into their cylinders? Or B) do I completely remove the pistons and clean the pistons, seals and cylinders the reassemble? What type of assembly lubricant do I use seals other then DOT 4 brake fluid?

  4. #4
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    Reputation: SteveUK's Avatar
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    I'd agree with 'A', although Isopropyl Alcohol is not good as it can dry out the seals. DOT fluid is OK. I use a silicone spray from the 3-In-One company (also makes WD40) and find it to work very well at both cleaning and lubricating. Extend the pistons as you describe, then spray the silicone into the caliper interior. Cotton buds are great for wiping around the edges of the pistons.
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    What luck for rulers, that men do not think - Adolf Hitler

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